Rocket engine construction



Jane 31, 1967 F. K. REINSTEIN ETAL 3,301,184

ROCKET ENGINE CONSTRUCTION Filed Oct. 7, 1963 INVENTORS Fredenck K. Reinssein 3V WiHiam G. Taylor ATTORNEYS United States Patent O 3,301,184 ROCKET ENGINE CONSTRUCTION Frederick K. Reinstein, Arleta, and William G. Taylor,

Palo Alto, Calif., assignors to Thiokol Chemical Corporation, Bristol, Pa., a corporation of Delaware Filed Oct. 7, 1963, Ser. No. 315,120 7 Claims. (Cl. 102-49) This invention relates to improvements for plural-stage rockets, and particularly to such rockets having a solidpropellant motor for the first stage and wherein the second stage may be ignited by the terminal combustion of the first stage.

One of the methods of increasing the useful energy of a rocket so that it may have greater range or greater capability in boosting heavy payloads is to decrease the weight of the inert parts of the rocket relative to the weight of the propellant. One of the recent proposals for accomplishing this objective in the case of plural-stage rockets having a solid-propellant motor for the first stage is to eliminate that portion of the first-stage case that would normally complete the pressure vessel at the forward end thereof-the forward end of the first-stage case being substantially continuous in form with the nozzle of the second stage, and the second stage being totally loaded with propellant, even into its nozzle, so that propellant is continuous from the forward end of the first stage into the second stage. In this arrangement, the second stage of the rocket would be automatically ignited by the terminal combustion of the first stage and the stage separation device could be so arranged that stage separation could be automatically effected after ignition of the second stage occurred. A considerable saving in weight of inert parts of the total rocket could be realized in this manner: (1) the weight of the forward end of the first-stage case would be eliminated, (2) the ignition device for the second stage would be eliminated, and (3) the weight of the electrical equipment associated with ignition of the second stage would be eliminated. However, there are certain disadvantages to this kind of rocket, due primarily to the fact that currently-available solid propellants do not have sufficient structural strength to contain the operating pressure of the first stage without some kind of reinforcement. It has been shown that rocket motor cases increase in volume when subjected to pressure; hence, there is danger that pressure created by the combustion of the first stage will be transmitted to the second stage of the rocket described, causing its case to enlarge and permit cracking of the propellant or extrusion of burning propellant from the first stage into the second stage prematurely. This could cause malfunction of the rocket in a number of ways: (1) the thrust of the first stage may become erratic as a result of its deformed burning surface, (2) cracking of the second-stage propellant may cause that stage to explode because of its greatly-increased burning surface, or (3) the second stage may be ignited prematurely. Also, this kind of rocket eliminates the possibility that the second stage motor be anything but a 100% loaded, solid-propellant rocket motor.

Our invention comprises essentially a lightweight pressure barrier fitted into the forward end of the first-stage case. This not only makes possible all of the savings in weight of the rocket described, but also, it permits use of either a liquid-propellant rocket motor or a solidpropellant rocket motor having a central combustion chamber for the second stage of the rocket.

An object of our invention, therefore, is to provide a device that will make the savings-in-weight of the pluralstage rocket described feasible with the use of currentlyavailable solid propellants.

Another object of the invention is to provide a device that will confine the operating pressure of the first stage of the rocket described.

Another object of our invention is to permit the use in a rocket of the nature described in a second stage which may be either a solid-propellant motor having a central combustion chamber, or a liquid-propellant motor.

Another object of the invention is to permit ignition of the second stage by the terminal combustion of the first stage without the possibility of premature ignition. Other objects and advantages of our invention will become apparent as the following description is read with reference to the accompanying drawings, wherein identical characters refer to corresponding parts throughout the several views.

FIGURE 1 is a perspective view of the rocket de scribed;

FIGURE 2 is a partial sectional view taken on the line 2-2 of FIGURE 1 showing the invention with the use of a solid-propellant rocket motor having a central combustion chamber as the second stage;

FIGURE 3 is a partially broken away perspective view of the barrier of the present invention removed from the rocket; and

FIGURE 4 is a view similar to FIGURE 2 showing how a second-stage, liquid-propellant motor may be used.

In the preferred form of the invention, illustrated in FIGURES 1 and 2, a rocket 6 comprises a solid-propellant first-stage motor 8, attached to a second stage solid-propellant motor 13. The first-stage 8 comprises a case 10 open at the forward end and substantially continuous in form with the nozzle 12 of the second stage 13 having a central combustion cavity 14 in its propellant 16. The outer skin of the casing of the first stage covers the nozzle of the second stage and terminates at the outer periphery of the casing for the second stage to permit the stages to separate. A stage-separation device 18 and a pressure barrier 20 are fitted into the forward end of the first stage.

The pressure barrier 20, as shown in FIGURE 3, consists essentially of a layer of urethane foamed resin 22 bonded to a plate 24- formed of bonded-together laminations of a polymerized, thermo-setting resin, such as phenolic, which are reinforced by glass fibers embedded in the laminations. The barrier 20 is formed to fit precisely into the forward end of the first-stage case and is bonded therein with a bonding agent such as that used to bond the laminations of plate 24 together such as, for example, epoxy resin. After the pressure barrier 20 is firmly fixed into the forward end of the first-stage case, the case is then loaded with propellant and the manufacture of the motor is completed in the usual manner. The preferred density of the foam portion 22 of the pres sure barrier 20 is approximately 40 pounds per cubic foot. An explosive fuse 26 is molded in the form of a loop inside of the foam layer 26 and connected to two heat-sensitive primers 28 that are positioned on the surface of the foam layer 22 toward the propellant 30 of the first-stage motor 8. The explosive fuse 26 and its primers 28 may be selected from many commercially-available fuses and primers. The explosive means could, in fact, be any detonating device capable of reacting to the heat of terminal combustion of the first-stage motor with sulficient force to shatter the pressure barrier 20 without damaging other parts of the rocket 6.

In the illustrated embodiment of the invention, the barrier 20 is designed to contain an operating pressure of approximately 750 p.s.i.g. and has the form of a truncated cone with sides inclined at 20 degrees to the center line thereof and a base 37.5 inches in diameter. The plate 24 having a thickness of 0.1 inch formed the smallest base of the truncated cone; the remainder comprising the 1.4-inch-thick layer 22 of foamed resin.

Approximately 270 grams of resin were used with approximately 32.1 grams of catalyst to form the layer 22. The weight-percentage composition of the resin was:

Percent Toluene diisocyanate 50 Castor oil 42.5 Polyethylene glycol 7.5

The weight-percentage composition of the catalyst was:

In the manufacture of the barrier 20, a mold was constructed having interior dimensions that conform to the dimensions of the required barrier. The plate 24 was then roughened with sandpaper on one surface and placed in the bottom of the mold with the roughened surface uppermost. The resin and catalyst were then poured into a mixer and thoroughly mixed until a uniformly whiteish appearance indicated that the foaming action had begun. This composition was then poured into the mold and allowed to foam until level with the upper edge of the mold. The explosive fuse 26 was then introduced into the foam in the form of a large loop, so that substantially the entire barrier could be exposed to the shattering action of the fuse upon detonation thereof; and the two primers, one at each end of the fuse, were carefully oriented on the top of the foam. The detonating fuse 26 comprised to 20 grains per linear foot of pentaerythrite tetanitrate encased in a lead tube, and is available commercially. Six to twelve inch lengths of glass fiber roving were then placed on top of the foam for reinforcement, and a flat lid, containing vents for the escape of excess foam, was securely fastened to the top of the mold. The mold was then placed into an oven and the foam was set by exposing it to a temperature of 160 F. for approximately 24 hours. The mold and its contents were then cooled; and the barrier was removed from the mold and bonded into the forward end of the rocket-motor case with an epoxy resin. After the bonding was firm, the rocket motor was loaded with solid propellant in the usual manner well known in the art.

If desired, the mold may be eliminated by foaming and curing the resin in situ in the forward end of the rocket motor.

In operation, the first-stage motor 8 may be ignited by a launcher-retained ignition device, not shown. When the propellant of the first-stage motor is nearly expended, the primers 28 react to the terminal heat of combustion to detonate the fuse 26 and shatter the pressure barrier 20. This allows hot gases from the first stage 8 to enter the second stage 13 to ignite the propellant 16 thereof. A heat-sensitive device 32 may be suitably located, such as near the ignition surface of the second-stage propellant 16 as shown in FIGURE 2, to actuate a stage-separation device 34 when the second-stage propellant 16 has been ignited. Devices 32 and 34 may be any stage-separation devices and their actuating means which are well known in the art, such as exposive bolts actuated by a voltagegenerating device. The fact that most currently-available solid propellants have very low rates of thermal conductivity is advantageous in making possible the use of the heat-sensitive primers 28, since these primers can be arranged and selected to react to the heat of combustion of the first stage motor when the propellant therein is almost consumed but when there is still enough pressure in the first stage motor to force hot gases through the aperture created by the shattering of the barrier 20 to ignite the second stage motor 12.

It may be noted that the only requirements that must be satisfied by the material from which the pressure barrier 20 is made are that (1) it must be light in weight relative to the parts of the rocket eliminated by its use, (2) it must be strong enough to complete the forward end of the first-stage case as a pressure vessel, i.e., it must be capable of containing the operating pressure of the first-stage motor, and (3) it must be frangible enough to be shattered by the explosive means without damaging other parts of the rocket. Therefore, although specific materials have been cited as the preferred form of the invention, any material having these properties may be used for the pressure barrier 20 without departing from the scope and spirit of the invention. For example, the pressure barrier 20 may be constructed of aluminum, a magnesim-aluminum alloy, and many different kinds of plastics such as acetates, acrylics, and phenolics.

Also, although the pressure barrier illustrated herein has the form of a truncated cone, it may be noted that the exact form of the barrier 20, as well as the optimum kind of material from which it is made will be determined largely in any given case by the characteristics peculiar to the rocket motor that is to be used for the first stage.

We claim:

1. In a plural-stage rocket wherein a first stage is a solid-propellant motor having a case open at the forward end thereof adjacent the rearward end of a second stage, said second stage containing a propellant and having a nozzle at its rearward end forming a continuation of the open end of the first stage, a pressure barrier fixed into said forward end to close said case and form a pressure vessel, said pressure barrier comprising (a) a light-weight frangible disk, and

(b) an explosive means therein having at least one detonating primer adjacent the solid propellant and detonated by the heat of terminal combustion of said first stage whereby to shatter said frangible disc and instantaneously open the forward end of the first stage and rearward end of the second stage whereby to ignite the propellant in the second stage, and means for separating the first and second stages responsive to ignition of said second stage.

2. A rocket in accordance with claim 1 wherein said explosive means comprises (a) a loop of explosive fuse embedded in said disk and (b) a heat-sensitive primer connected to said fuse and positioned to react to the heat of terminal combustion of said first stage.

3. A rocket in accordance with claim 1 wherein said disk comprises (a) a layer of urethane foamed resin, and

(b) a plate formed of bonded-together laminations of reinforced, polymerized resin bonded to said layer of urethane foamed resin.

4. A rocket in accordance with claim 3 wherein said laminations include glass fibers for reinforcement.

5. The rocket in accordance with claim 1 wherein said disk is made of a ma gnesium-aluminum alloy.

6. A plural-stage rocket comprising (a) a first-stage solid-propellant rocket motor having a case with a converging wall and open at the forward end thereof, a pressure barrier in the form of a lightweight frangible disk containing an explosive therein and located in the converging forward end of the case for the first stage,

(b) a second-stage solid-propellant motor having a central combustion chamber therein and a nozzle at the rear thereof with a diverging wall forming a continuation of the converging wall of the case for the first stage, and

(c) a stage-separation means, for separating said first and second stages, responsive to ignition of said second stage.

7. A plural-stage rocket comprising (a) a first-stage solid-propellant rocket motor having a case with a converging wall and open at the forward end thereof, a pressure barrier in the form of a light-weight frangible disk containing an explosive therein and located in the converging forward wall of the case for the first stage,

(c) a stage-separation means, for separating said first and second stages, responsive to ignition of said second stage.

References Cited by the Examiner UNITED STATES PATENTS 5/1960 Margulis et al. 10249 6/1961 Fox 102-49 (b) a second-stage liquid-propellant motor having a d BENJAMIN A. BORCHELT, Primary Examiner.

nozzle with a diverging wall forming a continuation of the converging forward wall of the case for the first stage, and

SAMUEL FEINBERG, Examiner.

V. R. PENDEGRASS, Assistant Examiner. 

1. IN A PLURAL-STAGE ROCKET WHEREIN A FIRST STAGE IS A SOLID-PROPELLANT MOTOR HAVING A CASE OPEN AT THE FORWARD END THEREOF ADJACENT THE REARWARD END OF A SECOND STAGE, SAID SECOND STAGE CONTAINING A PROPELLANT AND HAVING A NOZZLE AT ITS REARWARD END FORMING A CONTINUATION OF THE OPEN END OF THE FIRST STAGE, A PRESSURE BARRIER FIXED INTO SAID FORWARD END TO CLOSE SAID CASE AND FORM A PRESSURE VESSEL, SAID PRESSURE BARRIER COMPRISING (A) A LIGHT-WEIGHT FRANGIBLE DISK, AND (B) AN EXPLOSIVE MEANS THEREIN HAVING AT LEAST ONE DETONATING PRIMER ADJACENT THE SOLID PROPELLANT AND DETONATED BY THE HEAT OF TERMINAL COMBUSTION OF SAID 